The present invention relates to an apparatus for smoothing pressure pulsations in fluid flow lines. The invention finds particular application when used in conjunction with a liquid pump which is driven by a reciprocable air motor, wherein the air motor reciprocates through a predefined stroke and reverses direction through the same stroke in the other direction; a liquid pump is typically mechanically linked to this motion, thereby causing pressure fluctuations at each of the reciprocation changeover points. The effect of this operation on the fluid being pumped is to cause periodic pressure fluctuations in the fluid delivery lines. Such fluctuations are undesirable when smooth fluid delivery is desired, and are also undesirable because they may create undue wear on the delivery system. Under typical operating conditions a reciprocable pump is set to deliver liquid at some average pressure value under nominal flow rate conditions. Under these conditions, the instantaneous pressure of liquid delivery from the pump may exceed the average value by 10%-20% during one portion of the pump piston stroke, and may drop below the average pressure value by 10%-20% during another portion of the pump piston stroke.
Devices for minimizing pulsations in liquid delivery lines are known in the art. For example, U.S. Pat. No. 1,893,685, issued Jan. 10, 1933, discloses a diaphragm air chamber connected to a liquid delivery line, wherein liquid pressure surges are absorbed in the diaphragm chamber by displacing a volume of pressurized air. U.S. Pat. No. 1,767,100, issued Jun. 24, 1930, discloses a liquid chamber in combination with an air chamber for absorbing pulsations in a liquid delivery line. U.S. Pat. No. 4,445,829, issued May 1, 1984, discloses an enlarged chamber downstream of a liquid delivery pump, coupled with a gas-filled bladder for dampening pressure pulses which pass through the chamber. U.S. Pat. No. 3,188,975, issued Jun. 15, 1965, discloses a hydraulic piston connected to an air piston, wherein the hydraulic piston is responsive to hydraulic impulses, and causes the air piston to act against an air cushion, thereby diminishing pressure surges.